The present invention is concerned with binding partners (such as monoclonal or recombinant antibodies) for the thyrotropin receptor (TSH receptor or TSHR) and uses thereof.
Thyrotropin or thyroid stimulating hormone (TSH) is a pituitary hormone which plays a key role in regulating the function of the thyroid. Its release is stimulated by the hormone TRH formed in the hypothalamus and TSH controls the formation and release of the important, thyroid hormones thyroxine (T4) and tri-iodothyronine (T3). On the basis of a feedback mechanism, the thyroid hormone content of serum controls the release of TSH. The formation of T3 and T4 by thyroid cells is stimulated by TSH by a procedure in which the TSH released by the pituitary binds to the TSH receptor of the thyroid cell membrane.
In Graves' disease (a common autoimmune disorder) TSH receptor antibodies (TRAb) are formed and these autoantibodies bind to the TSH receptor in such a way as to mimic the actions of TSH, stimulating the thyroid gland to produce high levels of thyroid hormones. These autoantibodies are described as having stimulating activity. In some patients, autoantibodies bind to the TSH receptor but do not stimulate thyroid hormone production and are described as having blocking activity. (J Sanders, Y Oda, S-A Roberts, M Maruyama, J Furmaniak, B Rees Smith; “Understanding the thyrotrophin receptor function-structure relationship” Balliere's Clinical Endocrinology and Metabolism; Ed T F Davies 1997; 11 (3): 451-479; pub Ballière Tindall, London).
Measurements of TSH receptor antibodies are important in the diagnosis and management of Graves' disease and other thyroid disorders. Currently three types of assay are used to measure TSH receptor antibodies:
(a) competitive binding assays which measure the ability of TSH receptor antibodies to inhibit the binding of TSH to preparations of TSH receptor;
(b) bioassays which measure the ability of TSH receptor antibodies to stimulate cells expressing the TSH receptor in culture; and
(c) immunoprecipitation of TSH receptor preparations with TSH receptor antibodies.
Measurement of TSH receptor antibodies using such assays are described in references:—    J Sanders, Y Oda, S-A Roberts, M Maruyama, J Furmaniak, B Rees Smith; “Understanding the thyrotrophin receptor function-structure relationship” Balliere's Clinical Endocrinology and Metabolism; Ed T F Davies 1997; 11 (3): 451-479; pub Ballière Tindall, London.    Sanders, Y Oda, S Roberts, A Kiddie, T Richards, J Bolton, V McGrath, S Walters, D Jaskolski, J Furmaniak, B Rees Smith; “The interaction of TSH receptor autoantibodies with 125I-labelled TSH receptor”; Journal of Clinical Endocrinology and Metabolism 1999; 84 (10): 3797-3802.
It has been recognised for many years that human monoclonal antibodies to the TSH receptor derived from patients'lymphocytes would be valuable reagents for understanding the pathogenesis of Graves' disease and for developing new methods of measuring TSH receptor antibodies for example as replacements for TSH in competitive binding assays. Also, as the patient's serum TSH receptor antibodies are usually powerful thyroid stimulators (TSH agonists) stimulating human monoclonal TSH receptor antibodies would be valuable for in vivo applications when tissue containing the TSH receptor (eg thyroid tissue or thyroid cancer tissue) required stimulation. Furthermore, as some patient serum TSH receptor antibodies are powerful TSH antagonists (blocking antibodies) human monoclonal TSH receptor antibodies which are TSH antagonists would be valuable for in vivo applications when the activity of tissue containing the TSH receptor (eg thyroid tissue or thyroid cancer tissue) required inactivation or to be made unresponsive to TSH, TSH receptor antibodies or other stimulators.
It has also been recognised that one of the major advantages of human monoclonal TSH receptor antibodies over TSH in such in vitro and/or in vivo applications would be the relative ease with which antibodies can be manipulated. For example, manipulation of the TSH receptor binding region of the monoclonal antibodies so as to change their characteristics, such as affinity and biological characteristics including their degree of TSH agonist or antagonist activities. Also, monoclonal antibodies will have a much longer half life than TSH in vivo and this may have considerable advantages in certain in vivo applications. Furthermore, the half life of antibodies can be manipulated easily, for example antibody Fab fragments have a much shorter half life than intact IgG. These general properties of TSH receptor antibodies are described in the publications such as B Rees Smith, S M McLachlan, J Furmaniak; “Autoantibodies to the thyrotropin receptor”; Endocrine Reviews 1988; 9: 106-121; B Rees Smith, K J Dorrington, D S Munro; “The thyroid stimulating properties of long-acting thyroid stimulator yG-globulin subunits”; Biochimica et Biophysica Acta 1969; 192: 277-285; K J Dorrington, D S Munro; “The long acting thyroid stimulator”; Clinical Pharmacology and Therapeutics 1966; 7: 788-806.
A still further advantage of human monoclonal TSH receptor antibodies could be in their use to identify and provide new types of TSH receptor antibody binding sites. For example by the generation of antibodies to the regions of the human monoclonal TSH receptor antibodies which bind the TSH receptor. Some of the anti-idiotypic antibodies produced in this way could have potential as new ligands for assays of TSH receptor antibodies, TSH and related compounds. Also they may be effective agents in vivo for regulating the action of TSH receptor antibodies, TSH and related compounds.
Other methods of identifying and providing new types of antibody binding sites using monoclonal antibodies are well known. For example by antibody screening of phage-displayed random peptide libraries as described by J C Scott and G P Smith; “Searching for peptide ligands with an epitope library”; Science 1990; 249 (4967): 386-390 and M A Myers, J M Davies, J C Tong, J Whisstock, M Scealy, I R MacKay, M J Rowley; “Conformational epitopes on the diabetes autoantigen GAD65 identified by peptide phage display and molecular modelling”; Journal of Immunology 2000; 165: 3830-3838. Antibody screening of non-peptide compounds and libraries of non-peptide compounds can also be carried out.
New types of TSH receptor antibody binding sites identified and provided using these procedures may also be useful as new ligands in assays for TSH receptor antibodies, TSH and related compounds. Furthermore they may be effective agents in vivo for regulating the action of TSH receptor antibodies, TSH and related compounds.
In view of the potential value of human monoclonal TSH receptor antibodies there have been considerable efforts over many years to produce such antibodies (see for example B Rees Smith, S M McLachlan, J Furmaniak; “Autoantibodies to the thyrotropin receptor”; Endocrine Reviews 1988; 9: 106-121. However, to date these efforts have been unsuccessful (see for example S M McLachlan, B Rapoport; “Monoclonal, human autoantibodies to the TSH receptor—The Holy Grail and why are we looking for it”; Journal of Clinical Endocrinology and Metabolism 1996; 81: 3152-3154 and J H W van der Heijden, T W A de Bruin, K A F M Gludemans, J de Kruif, J P Banga, T Logtenberg; “Limitations of the semisynthetic library approach for obtaining human monoclonal autoantibodies to the thyrotropin receptor of Graves' disease”; Clinical and Experimental Immunology 1999; 118: 205-212).